The present disclosure relates to a secondary drive device of a mobile working appliance, such as, for example, a tractor for the connection of working machines, and to a method for coupling and/or uncoupling a working machine to/from the secondary drive device.
Mobile working appliances, such as tractors, but also heavy goods vehicles with additional functions (additional assemblies), such as winches, cranes and such like machines, are usually equipped with a secondary drive, via which the secondary assembly can be connected to the engine (internal combustion engine) of the mobile working appliance as an energy source. Such a secondary drive has what is known as a power take-off shaft, the free end of which is mostly designed with a spline shaft profile for transferring a torque and which either is designed in a separate drive shaft of the engine (engine power take-off shaft which is connected directly to the engine and runs correspondingly to the engine rotational speed) and constitutes an output shaft connectable via a clutch to the transmission of the mobile working appliance (transmission power take-off shaft which is connected to the engine via the clutch and transmission and can be operated with different nominal rotational speeds) or is provided as a connecting shaft connected to the driving axle of the mobile working appliance (directional power take-off shaft which is coupled by means of toothing to the drivetrain of the wheels, so that the rotational speed rises with an increase in driving speed).
In practice, transmission power take-off shafts, that is to say those power take-off shafts which are selectively connectable to the transmission of the working appliance via a clutch, have proved acceptable, since these can be selectively activated/deactivated via the clutch and moreover, in contrast to the power take-off shafts connected to the driving axle, can generate torque independently of the propulsion speed of the working appliance.
A secondary drive device of the transmission power take-off shaft type is known from the prior art, for example according to DE 28 13 991 C2. Accordingly, a tractor as a mobile working appliance is equipped with an engine transmission, to which a secondary drive shaft can be coupled, to which, in turn, an additional assembly, for example for agricultural use, can be connected. For this purpose, a clutch is provided, which, in the engaged state, can transfer a nominal torque to the power take-off shaft. The operative connection between the clutch and transmission is configured such that two different rotational speeds can selectively be picked off from the transmission. To actuate the clutch, a hydraulic system is provided, which can be activated via an electric/electronic control unit and is fluid-connected to the clutch, so that the clutch is engaged and disengaged by a driver as a function of an actuating signal.
It has been shown that, in secondary drive devices in general and particularly of the transmission power take-off shaft type, a problem arises when the additional assembly is coupled and uncoupled to/from the power take-off shaft, in that the spline shaft profile of the power take-off shaft is randomly in a rotary position in which it is not possible to plug on or plug in an input shaft of the additional assembly, for example when the teeth of the two shafts are aligned with one another (that is to say, when the teeth of the power take-off shaft impinge on the teeth of the drive shaft of the additional assembly). This situation also often arises when the additional assembly is uncoupled, the spline shaft profile or spline shaft connection is under (torque) load, as before, and therefore the two shafts are braced with respect to one another such that it becomes impossible to separate the two shafts.
Even when the clutch is disengaged, manual rotation of the power take-off shaft, even with the aid of more or less suitable tools, is often possible only with difficulty or not at all, since the resistance of the power take-off shaft mounting is too great. The same also applies, as a rule, to the additional assembly. The correct rotary position of the power take-off shaft with respect to the input shaft of an additional assembly can therefore sometimes be achieved only with difficulty (randomly) or after a great amount of time has been expended.
Basically, there is always the possibility of setting the power take-off shaft in (dummy) rotation by engaging the clutch and consequently influencing the rotary position at renewed standstill. However, the final rotary position of the power take-off shaft resulting from this at renewed standstill is essentially random, since, for safety reasons, when an activating switch of the control unit is actuated in order to put the power take-off shaft into operation, engagement of the clutch is triggered only with a predetermined time delay (usually 2 sec), and also the disengagement of the clutch does not take place with such accuracy that the final rotary position of the power take-off shaft can be predetermined.
In view of this problem, an object of the present disclosure is to provide a secondary drive device of the transmission power take-off shaft type, which has higher functionality. One aim of the disclosure is in this case, in particular, to improve the convenient handling of the secondary drive device during coupling and/or uncoupling of an additional assembly.